Electropneumatic brake control system parking brake

ABSTRACT

A braking system including a brakepipe control valve which controls pressure on a brakepipe in response to braking pressure signal from an electropneumatic converter. An electropneumatic cutoff valve connects the control valve to the brake pipe. A controller controls the converter and cutoff valve. A parking brake system and retarder control system are also included and are controlled by the controller.

This is a Continuation of application Ser. No. 08/260,376, filed Jun.14, 1994, now U.S. Pat. No. 5,494,342.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to an improved train brakesystem and more specifically to an electropneumatic brake system forintegral trains.

An integral train is a train on which the motive power and carryingunits are integrated into a single unit, with systems shared betweensubunits. It is distinct from a conventional train in that it does notrequire that motive power be utilized into a separable locomotive, andthat carrying parts of the train are not required to be switchable infreight yards nor to be capable of exchange between trains. One exampleof an integral train is the Iron Highway--a train consisting of one ormore elements. Each element composed of integrated power and carryingplatforms with a control cab at each end of the element. Each elementconsists of one or two power cabs and a fixed number of platforms. Theplatforms and power cabs are articulated together in order to bothreduce the normal slack between the cars and provide a continuous flatdeck over the length of the continuous platform. The reduction of theslack results in a corresponding reduction in the dynamic forces whichthe cars are required to withstand during the run in and out of thetrain slack. The reduction of the dynamic forces and elimination ofswitchyard impacts allows for the use of lighter cars, which allows foran increase in the cargo weight for a given overall train weight andtherefore an increase in train efficiency. Additional improvements inefficiency are obtained through the truck design and from other sources.

An example of an integral train is described in my prior U.S. Pat. No.4,702,291. Because of this unique design of integral trains, thereexists an opportunity to design a brake control system without thelimitation of standard freight brakes. The system should include theability to control the brakes throughout the integral train, providecontrol of a retarder for the propulsion transmission, operate on theparking brakes as well as provide the appropriate operation during anemergency towing by a conventional locomotive.

One example of a computerized brake control system is U.S. Pat. No.4,402,047 to Newton et at. This is an electropneumatic system which usestransducers and a feedback loop to control the brakes of a singlevehicle which in this case is generally the locomotive of a conventionaltrain. The controller of this system uses pressure signal feedbacks tothe computer which compares these to a target and makes fine correctionsto an output device to provide variations of the signal to maintain theappropriate brake pressure in a brake cylinder. Other examples ofelectropneumatic brake systems and electrically assisted application andrelease for fluid pressure brake systems, for example, U.S. Pat. Nos.4,052,110 and 4,076,322.

Thus, it is an object of the present invention to provide an improvedbrake control system for integral trains.

It is another object of the present invention to provide anelectropneumatic brake control system which will control the brakepipeand parking brakes.

It is another object of the present invention to provide anelectropneumatic control system which will permit simultaneous brakepipereduction and restoration at a number of points along a train.

It is a further object of the present invention to provide a brakecontrol system which controls the brakepipe, a parking brake and apropulsion transmission retarder.

A still further object of the present invention is to provide a brakecontrol system which can be used with a conventional locomotive duringan emergency tow.

These and other objects are achieved by a system including a controlvalve for controlling pressure on the brakepipe in response to a brakecontrol signal, a cut-off valve connecting the control valve to thebrakepipe and a converter for converting digital values of electricbrake signals to discreet pneumatic brake control signals for thecontrol valve. A controller provides the digital electric brake signalsfor controlling brakepipe pressure. The converter valve is a pilot valvehaving a plurality of solenoids responsive to the digital values. Thisallows accurate repeatable control and produces the discreet pneumaticbrake control signals. The unique converter, in response to digitalsignals, allows the appropriate control of the brakepipe pressurewithout the need for any electronic feedback signals. The control valveincludes a first pressure sensitive element responsive to a firstpressure signal to maintain the brakepipe at a fixed first pressurevalue and a second pressure responsive element responsive to thepneumatic brake control signal from the converter to reduce pressure inthe brakepipe to values which are discreet fractions below the firstvalue. The first pressure sensitive element compares brakepipe to thefirst pressure signal and the second pressure sensitive element isconnected to the first pressure element and reduces the effect of thefirst pressure signal in response to the pneumatic brake control signal.A feeder valve determines the first pressure signal. The pneumatic brakecontrol signal varies in a range from zero to the first pressure signaland a ratio of the response of the first and second pressure sensitiveelements defines the brakepipe service braking pressure range.

For integral trains, the electropneumatic brake control system includesat least two brakepipe control systems, each including a control valve,a cut-off valve, a converter valve and a controller. The secondbrakepipe control system may include transducers for sensing the firstpressure signal provided to its control valve as a reference and thebrakepipe pressure. The controller of the second system, and furthersystems on the common brakepipe which are the trailing or slave systems,doses its cut-off valve at a difference between the measured firstpressure signal and measured brakepipe pressure. This prevents thesecond brakepipe control system from attempting to charge the brakepipewhile the lead or master or first brakepipe control system is attemptingto reduce the pressure in the brakepipe control system.

Each system includes an electropneumatic emergency vent valve connectedto the brakepipe and the controller controls the cut-off valve to closeand controls the electropneumatic emergency vent valve to open for anemergency braking. Also, a pneumatic emergency vent valve is connectedin response to an emergency brakepipe pressure in the brakepipe to ventthe brakepipe. A transducer senses an emergency brakepipe pressure inthe brakepipe and the controller controls the cut-off valve and theelectropneumatic emergency vent valve in response to an emergency inputfrom the transducer or an emergency input from an operator.

This system also includes a pneumatic parking brake system responsive tobrakepipe pressure for applying and releasing a parking brake so thatparking brake will be automatically released by a towing locomotive, butnot be applied at any time by the controller as during normal operation.An electropneumatic parking brake valve is connected to the parkingbrake by the pneumatic parking brake valve and is controlled by thecontroller to apply and release the parking brake. The system includes aretarder valve connected to a retarder control actuator on poweredplatforms. The controller controls the retarder valve to providepneumatic retard signals to operate the retarder actuator to achievedynamic braking. An interlock valve, in the pneumatic circuit of thebrake cylinder, is responsive to file retarder control pipe signals toreduce the brake cylinder pressure when the wheels associated with aparticular brake cylinder are being braked by the retarder. Thisprevents over braking and wheel slip.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a propulsion system incorporating theprinciples of the present invention.

FIG. 2 is a schematic piping diagram of the brake system according tothe principles of the present invention.

FIG. 3 is a block diagram, partial cut-away schematic of anelectropneumatic brake control manifold system for application at thecontrol ends of an element incorporating the principles of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The electropneumatic brake control system of the present invention willbe described specifically with respect to an integral train described inU.S. Pat. No. 4,702,291 which is incorporated herein by reference, butis only by way of example. The brake control system may be used in anytrain system. The integral train includes a plurality of train segmentsand each segment includes a pair of control cabs at each of the segmentwith a plurality of cars or platforms forming a continuous decktherebetween. As illustrated in FIG. 1, a segment is shown as having twocontrol cabs 26 and 28 with a plurality of cars 30 there between.

The control cabs 26 and 28 are not control cabs in the conventionalsense. The propulsion system 50 is considered a distributive propulsionsystem as illustrated in FIG. 1. The control cabs 26 and 28 include amechanical engine 52 driving an electrical alternator 54. The output ofthe alternator 54 is three phase current whose frequency and voltage area function of the speed of the engine 52. This current is transmitteddown a three phase wire system 56 to a plurality of electric motors 58distributed throughout the cars 30. Each of the electric motors 58 areconnected via a hydraulic retarder 59 to a respective transmission 60which includes a directional control reversing gear 62. The output ofthe directional control reversing gear drives a differential 64 to whicha pair of axles 65 and wheels 66 are connected.

Each of the control cabs 26 and 28 include a controller 68 which cancontrol the throttle position of all of the engines 52 based on acontrol handle position selected by the operator in one cab. Thecontroller 68 also provides control signals via line 70 to thetransmission 60 and the reversing gear 62. A train speed sensor 72 on anon-powered, non-braked axle provides an input signal to controller 68.The controller 68 selects the gears of the transmission and the shiftpoints as a function of the measured speed of the train and the throttlesetting. A communication line 82 interconnects the controller 68 on thecabs 26 and 28. The interconnection, protocol and the selection of thelead-trail relationship is described in the aforementioned patent. Thecontroller 68 provides control signals to the pneumatic brake systemthrough electric brake interface 90.

The system just described, other than the retarder 59, are described inthe aforementioned patent and the same reference numbers and symbols areused so easy reference can be made to the details described therein. Allof the elements of the present invention will have a reference number of100 or higher.

An electropneumatic brake control system is illustrated in FIG. 2 asincluding brake control system 200, the details of which will bedescribed in FIG. 3. A brakepipe 100 and a main reservoir or supply pipe102 run throughout the train and pneumatically interconnect the brakecontrols on each of the cam. Air for the main reservoir is supplied fromeither a compressor system or in the case of a failed local compressor,by the train line main reservoir pipe from other operative compressorsin the train. In the event the train is being towed by conventionallocomotive or train, air may be supplied to the system through both aconnection to the locomotives main reservoir pipe and to the brakepipe100 through a glad hand. In the event that the integral train elementmust be towed behind a conventional car (which has no main reservoirconnection) rather than a locomotive, air from the brakepipe will chargethe main reservoir system through a charging choke 240 and check valve238 in the brakepipe control system 200 to be described with respect toFIG. 3.

A combined control and relay valve 104, for example, model KE-1 from NewYork Air Brake is connected to the brakepipe 100 at various cars throughthe train. The control and relay valve 104 need not be provided at eachcar and may be spaced for example, at every fourth car. A reservoir 106is connected to the control/relay valve 104 by line 108 and is connectedto the main reservoir pipe 102 by line 110. The output of thecontrol/relay valve 104 is connected to the brake cylinders 118 by line112, load proportioning valve 114 and line 116. A load sensing element120 is shown connected to the proportioning valve 114.

The brake control system 200 is connected to the main reservoir pipe 102by line 122 and to the brakepipe 100 by line 124. Line 126 connects thebrake control system 200 to the parking brake 130 via a double checkvalve 128. The parking brake 130 is in a combined housing with theservice brake applicator 118. This combined structure is a well knowndevice such as an MGM TYPE R 3036 GT brake chamber from MGM Brakesdivision of Indian Head Industries, and is provided on the cars whichhave the propulsion units. As will be described below, the parking brakeis a spring applied brake and the pressure maintains the parking brakereleased. The double check valve 128 holds the parking brake in itsreleased position if the normal brakes 118 are applied from the servicebrake line 116 even though parking brake release line 126 may be a lowerpressure.

Another output of the brake control system 200 is a retard actuator 132connected to a lever of the retarder 59. As with the parking brake, theretarder 59 are only provided on those cars which have a propulsioncomponent. A dynamic interlock 136 is provided between the brake line112 and the combined control and relay valve 104 of the powered cars andis connected to the retarder control pipe 132. The retarder controlsignal on pipe 132 controls the interlock 136 to reduce the brakecylinder signal on line 112 of the motorized cars with an increasedretarder control signal which increases dynamic braking. Thiscoordinates the mechanical braking of the wheels with the transmissionbraking of the propulsion system on the motorized cars to prevent overbraking and wheelslip. The non-motorized cars do not have an interlock136. A typical interlock valve may be a H-5 relay valve available fromNew York Air Brake.

A vent valve 138, for example, type KM-2 available for New York AirBrake, senses a signal on the brakepipe 100 and vents the brakepipe 100upon sensing an emergency condition. These vent valves 138 are placedthroughout the train at intervals, for example, every other car.

A brake control unit 200, combining the commanding pneumatic valves forthe present system is illustrated in FIG. 3 as including a manifold 202connected to the main reservoir pipe by line 122, retard control pipe132, brakepipe by line 124 and parking brake release pipe 126. A feedvalve 204 connected to the manifold 202 and provides a regulatedpressure at brakepipe full release value to the brakepipe pressurecontrol system and the parking brake release system. A main reservoirtransducer 206 and feed valve transducer 208 are connected to thecontroller 68 through the brakepipe interface 90. A brakepipe controlvalve 210 receives a first pressure signal, which is the feed valveoutput, and a second pressure signal from brake signal converter 212 tocontrol the brakepipe pressure on brakepipe line 124. The brake signalconverter 212 is a electropneumatic device which converts digital valuesof electric brake signals from the controller 68 to discreet pneumaticbrake control signals for the control valve 210. As explained in detailbelow, the brake signal converter 212 is a seven-step pilot valve havingthree solenoids which produces the second pressure signal without thenecessity of feedback to the controller 68.

An electropneumatic brakepipe cut-off valve 214 connects the brakepipecontrol valve 210 to the brakepipe line 124. A brakepipe transducer 216and a brakepipe pressure switch 218 are provided on the manifold andprovide feedback signals to the controller 68 for use in signallingconditions to the Engineer and for operating a troubleshooting computer.As will be discussed below, the brakepipe transducer 216 and thebrakepipe pressure switch 218 in combination with the brakepipe cut-offvalve 214 controls the trailing or slave brakepipe control system 200 tocut-off at a pressure below that of the master or lead unit. Thisprevents the slave or trailing unit from attempting to charge thebrakepipe while the master or lead unit is diminishing the brakepipepressure for a brake application.

An electropneumatic emergency valve 220 is under the control of thecontroller 68 to electrically vent the brakepipe line 124 at all cabs inthe train simultaneously. This is a backup to the all pneumaticemergency brake system. A vent valve 222 provides positive venting ofthe brakepipe line 124 in response to either a break-in-two or anoperator initiated emergency brakepipe application on the brakepipe 100.

As previously discussed, the parking brake 130 is a spring applied,pressure released parking brake. Parking brake relay valve 224 isresponsive to brakepipe pressure to provide a signal from the feed valve204 to the parking brake release pipe 126. An electropneumatic parkingbrake release valve 226, under the control of the controller 68, canalso control the applying and release of the parking brakepneumatically. A parking brake release pipe pressure switch 228 providesfeedback to the controller 68.

A retarder control 230 is also provided on the manifold 202. It includesan electropneumatic retarder release valve 232 and an electropneumaticretard application valve 234. A retarder control pipe transducer 236 isalso provided. These three elements are electrically controlled with theretarder feedback signals to the controller 68 and is used to producefour pressure levels in the retarder control pipe at, 33%, 66% and full.

A charging choke valve 238 and a charging choke 240 are also provided onthe manifold 202 and connect main reservoir passage 242 and brakepipepassage 244 in the manifold 202. This allows the air supplied by aconventional locomotive which might be used to tow the train to chargethe system through a gladhand to the brakepipe and to charge the mainreservoir system through the charging choke 240 and choke valve 238.

The feed valve 204 connects the main reservoir pipe passage 242 and thefeed valve passage 246 via feed valve seat 248. The feed valve 204illustrated is a high capacity locomotive type feed valve for example, atype F-6, but may be an NS-1 pressure regulator. The feed valve 204provides a regulated first pressure signal representing a brakepiperelease value. The feed valve passage 246 is connected to the feed valvetransducer 208 and the brake signal converter 212 and the brakepipecontrol valve 210.

BRAKEPIPE CONTROL

The brakepipe control valve 210 has a first pressure response member ordiaphragm 250 with a feed valve chamber 252 on its topside and a brakesignal chamber 254 on its bottom side. The feed valve chamber 252 isconnected to feed valve passage 246 and the brake signal chamber 254 isconnected to brake signal passage 256 by choke 258 and provided as aninput to the brakepipe cut-off valve 214. A second pressure responsemember or diaphragm 260 has a brake control signal chamber 262 on itsbottom side connected by a brake control signal passage 264 to theoutput of the brake signal converter 212 and an atmosphere chamber 266is on the other side connected to atmosphere port 268. An interconnectmechanism 270 interconnects the second pressure responsive member 260 tothe first pressure responsive member 250. Since the brake control signalchamber 262 moves the second pressure response member 260 upward, itdiminishes the effect of the feed valve pressure in the feed valvechamber 252. This allows the balance of pressure responsive members at abrake signal chamber less than the feed valve chamber. Stem 272connected to the first pressure response member 250 operates a brakeapplication valve 274 which interconnects an atmosphere port 276 and thebrake signal passage 256 and a release valve 278 which interconnects themain reservoir passage 242 and the brake signal passage 256. Thebrakepipe control valve 210 is a standard brakepipe control valve withthe addition of the second pressure responsive member 260 and theinterconnecting mechanism 270 and may be for example, a modified NY-2available from New York Air Brake and designated NY-2B by that company.

The brakepipe signal on brakepipe signal passage 256 is connected to thebrakepipe line 124 by a diaphragm valve 280 of the brakepipe cut-offvalve 214. The top chamber 282 above the diaphragm 280 is controlled bya dual seat electromagnetic valve element 284 which connects the chamber282 either to the feed valve signal on passage 246 or atmosphere port286 via passage 288. This allows the controller 68 to electricallycontrol the connection of the brakepipe signal from the control valve210 to the brakepipe line 124 as will be described below.

Converter valve 212 receives the feed valve pressure 246 at its inputsand provides at its output 264 a specific percentage value of the supplyor feed valve pressure as a brake control signal to the brake controlsignal chamber 262 of the control valve 210. Three solenoids on theconverter valve 212 control the inputs to three diaphragms 290, 292 and294 which are ratioed to provide the desired progression. Thesediaphragms are interconnected mechanically to each other and valve 296to be balanced against the feed valve pressure on passage 246 to providethe digital signal on the brake control signal line passage 264. Theconverter valve 212 is a well known valve, for example, a seven-steppilot valve, model KBR XI-T from Knorr Bremse AG.

The electropneumatic emergency valve 220 has a solenoid valve element300 which interconnects an atmosphere port 302 to the brakepipe passage244 to vent the brakepipe to cause an emergency condition under thecontrol of the controller 68.

The brakepipe control operates as follows:

CHARGING (Leading Cab)

When the driver on the leading cab calls for brakes released, thebrakepipe cut-off valve 214 is energized, and all three pilot solenoidson the converter valve 212 are de-energized. Thus flow from thebrakepipe control valve 210 to brakepipe line 124 is unrestricted. Noair, however, is provided to the reduction or brake control signalchamber 262 of the control valve 210.

Feed valve air on passage 246 is, however, provided to the top chamber252 of the large control diaphragm 250 forcing it downward and openingthe release valve 278. This action allows air from main reservoirpassage 242 to pass into the output chamber of the control valve andsupply the brakepipe line 126 while at the same time entering thechamber 254 beneath the large control diaphragm 250 urging it upward.When brakepipe pressure rises to equal the value of the feed valvepressure on top of the diaphragm 250, the operator or valve stem 272will move up, closing the release valve 278 and cutting off further flowof main reservoir air passage 242 to the brakepipe line 124 at feedvalve or full release pressure.

CHARGING (Trailing Cab)

Operation of the converter valve 212 and brakepipe control valve 210 ontrailing manifolds is identical to that on the lead except that whenbrakepipe pressure rises to within, for example, 2.0 PSI of feed valvesetting, the brakepipe cut-off valve 214 will be de-energized by itslocal controller 68, stopping the local charging of the brakepipe line124. Thus preventing slight differences in feed valve settings on theseveral manifolds in a train from setting up a condition where one partof the train attempts to charge brake pipe while another locationdischarges it.

BRAKE APPLICATION (Leading Cab)

When the driver wishes to apply the brakes, the leading controller 68calls for one of the discreet levels of braking and will signal allmanifolds to open the brakepipe cutoff valves 214 and to output therequired pressure to brakepipe by energizing the appropriate solenoidvalves on the converter 212.

At the leading manifold, the solenoid energization pattern will causethe converter valve 212 at each manifold to produce an output pressureproportional to the desired increase in brake effort. This pressure willbe transmitted to the reduction control chambers 262 of the brakepipecontrol valves 210, where it will urge the stem 272 of this valveupward. This action opens the internal brakepipe exhaust or applicationvalve 274, causing brakepipe pressure (and hence the pressure beneaththe feed valve diaphragm) to drop in proportion to the increased signalfrom the converter valve 212.

Since the area of the second or reduction pilot diaphragm 260 is only28% of that of the first or main diaphragm 650, and since feed valvepressure applied to the reduction chamber 202 will place on the stem 272in the upward direction 28% of the downward force applied by the feedvalve pressure acting on the top chamber 252 of the main diaphragm 250.Thus with the exhaust or application valve 274 opened as described,brakepipe pressure will reduce until the stem 272 balances at a value72% of feed valve pressure, whatever this pressure may be. For example,a 90 PSI feed valve setting would have a 65 PSI brakepipe pressure atfull service reduction.

In the case of a less than full service (level 6 for example), the brakecontrol signal and resulting brake pipe reduction would be in proportionto the brake level called for.

BRAKE APPLICATION (Trailing Cab)

When braking is called for, all manifolds on the train receive the sameconverter valve energization pattern for the three solenoids, and thusproduce the same brake pipe reduction signal to chamber 262 of thecontrol valve 210. On trailing units, however, the local controller 68looks up the proper brakepipe pressure corresponding to the levelcommand and actual feed valve setting, and de-energizes the brakepipecut-off valve 214 when actual brakepipe pressure measured by transducer216 has fallen to within, for example, 2 PSI of this value. This allowsbrakepipe pressure maintaining to be controlled by the lead manifoldonly. In the event that surge effects cause brakepipe pressure to riseto a value greater than, for example, 3 PSI above the target, thebrakepipe cut-off valve 214 will re-open and assist the lead inmaintaining the reduction.

Should brakepipe pressure fall below the target value, however, thebrakepipe cut-off valve 214 will not re-open to maintain brakepipepressure unless the difference is again greater than 2 PSI since this isaccomplished from the head end.

Should the driver call for further brakepipe reduction by changing thecommand signal, the local controller 68 at all manifold locations willall open their respective brakepipe cut-off valves 214 to permit thenewly commanded value of brakepipe pressure to be rapidly andsimultaneously established at each location on the train.

EMERGENCY BRAKE APPLICATION (Driver Commanded)

When the driver calls for an emergency application, local brakepipeventing at an emergency rate is initiated mechanically by the MasterController mechanism, and an electrical signal is sent to all controller68 signalling their respective manifolds to dose the brakepipe cut-offvalve 214, and open the emergency valve 220. This latter action willtrip the pneumatic vent valve 222 on each manifold, thus initiatingadditional serial venting of the brakepipe 100 to speed up theapplication of brakes. Dynamic braking will be maintained in effectduring an emergency application.

EMERGENCY BRAKE APPLICATION (Break-In-Two)

When the brakepipe is opened by any means other than the MasterController, serial venting of brakepipe 100 will be initiated by thevent valves 138 and 222. When the vent valve 222 on any manifold trips,the reduction of brakepipe pressure will be noted by the brakepipefeedback transducer 216, which is placed in dose proximity to the ventvalve 222 so that brakepipe feed from passage 256, will not overcome theability of the system to note the initiation of an emergency reductionof brakepipe pressure.

When an emergency condition is thus found to exist, the controller 68communicates this fact to all other controllers 68 and at the same timecuts off brakepipe charging (if in effect) by cutoff valve 214 and opensthe local emergency valve 220. This action is repeated by allcontrollers 68 receiving the electrical emergency signal from whicheverlocation first noted the emergent, thus greatly speeding the applicationof brakes on the train.

It should be noted that when the train is being towed by conventionalequipment, all controls are dead and brakepipe cutoff valves 214 are allclosed. Thus, as no air can be fed to the brakepipe from the manifold202, there is no need for direct pneumatic brakepipe cutoff by cutoffvalve 214 to permit towing.

PARKING BRAKE CONTROL

The parking brake relay valve 224 includes a diaphragm 304 whose upperchamber 306 is connected to the brakepipe line 124 by brake line passage244. The parking brake release valve 226 is a solenoid controlled doubleseat valve 322 which connects the parking brake release signal passage320 to either the feed valve passage 246 when de-energized or toatmosphere port 324 when energized. A spring 308 below the diaphragm 304forces the diaphragm 304 against the brakepipe pressure. An actuator orvalve stem 312 interacts with a dual seat valve 314 to connect to thebrakepipe release passage 316 either to an atmosphere port 318 or theparking brake release signal passage 320 connected to the parking brakerelease valve 226.

The parking brake control operation is as follows:

PARKING BRAKE APPLICATION (Operator Controlled)

When service brakes are fully charged and released, the driver may wishto apply parking brakes to hold the train for test purposes. This isaccomplished by turning the "Parking Brake" switch on the MasterController. Thus causing the controller 68 to signal all manifolds toenergize their parking brake release valves 226 connecting passage 320to atmosphere and vent parking brake release pipe 126 to atmosphere.This vents the spring brake chambers 130 on the individual trucks andthe spring applies the parking brakes.

PARKING BRAKE RELEASE (Operator Controlled)

To release the parking brake once brakepipe 100 is charged, the driverturns the parking brake switch to release, signalling all controllers 68to de-energize their parking brake release valves 226. This per, nitsfeed valve air on passage 246 to pressurize the parking brake releasepipe 126 which is connected from each manifold to the motorized trucks.At the individual trucks, this pressure fills the spring brake actuators130, compressing their application springs and releasing the parkingbrakes.

PARKING BRAKE APPLICATION (Automatic)

When brakepipe pressure falls below 30 PSI for any reason, the relayvalve 224 switches to automatic application position (shown) cutting offthe supply of feed valve on passage 320 to the parking brake releasepipe 126, and connecting this pipe 126 to atmosphere at 316. Thisenables automatic parking brake application. At the individual trucklocations, brake cylinder pressure is double checked 128 into the springchambers, holding them released if normal brakes are applied, as theyshould be at low brake pipe pressure.

In this condition, if after a period of time the brake cylinder pressurefalls off due to leakage, spring chamber pressure will be lost and asthe service brake becomes less effective, the spring parking brake willautomatically take over maintaining the train safely held from motion.

PARKING BRAKE RELEASE (Automatic)

When brakepipe pressure is restored, whether from a towing conventionaltrain or from restarting a shut down train, brakepipe pressure will comeup and, with the control valve 104, so will service brake cylinder 118pressure. When brakepipe pressure rises above 30 PSI, the parking brakerelease relay valve 224 will switch and re-establish communication withthe parking brake release valve 226. Thus driver control of the parkingbrake by the controller 68 is restored.

PARKING BRAKE OPERATION (Dead in Tow)

Automatic operation of the parking brake remains unchanged from thatdescribed above when the integral train is being towed by a conventionaltrain. It is only necessary to connect the conventional train's brakepipe hose to that on the adapter coupler and release brakes in theconventional manner. Charging brakepipe 100 via 124 will charge the mainreservoir system through the manifold mounted charging choke 240 andcheck valve 238, providing a source of feed valve pressure to theparking brake release circuit. When brakepipe pressure rises above 30PSI, the parking brake relay 224 will connect the parking brake releasepipe 126 to this circuit. Thus, air at brake pipe pressure will flowthrough the feed valve 204, parking brake release valve 226, and theparking brake relay 224 to the parking brake release pipe 126. Whenbrake pipe pressure has risen sufficiently to release the service brakes118, the spring brake chambers 130 will be charged and parking brakeswill release as well.

When the integral train has been moved by conventional equipment to adesired location, the air brakes should be set in emergency. This willswitch the parking brake relay 224, venting the parking brake releasepipe 126 at all manifolds and permitting the spring brake 130 to applyas cylinder pressure is lost on the individual trucks. This provides thesame or better protection as an applied handbrake on conventionalequipment would.

RETARDER CONTROL

The motorized cars are each equipped with a hydraulic brake such as ahydraulic retarder or an eddy current brake 59 working on the tractionmotor input shaft to the transmission 60 to achieve dynamic braking.Control of retardation effort is extremely simple, requiring only thatthe pneumatic retarder pipe 132 be charged to a pressure proportional tobrake effort desired. The controller 68 will call for three levels ofretarder pipe pressure to be maintained very roughly at plus or minus15% of nominal pressure. If a calculation by the central tractioncomputer shows that full retarder control pipe pressure (or thecalculated maximum allowable pressure) will not produce the desiredretardation, then a further service brake application sufficient, whencombined with retarder action, to produce the commanded result, will bemade. On powered cars only, the brake cylinder pressure inhibit orinterlock valve 136 is interposed between the control valve 210 andbrake cylinder pipe 112. The interlock valve 136 suppresses brakecylinder supply by an amount proportional to retarder control pipepressure so as to prevent overbraking and wheelslip on powered axles.

The manifold's retarder control group 230 retard application valve 234admits air to the retarder pipe 132 via retard passage 236 until thecontroller 68 terminates charging, based on information from theretarder pipe transducer 236, at the charging high level of the retarderpipe dead band. If after termination of charging, retarder pipe pressurefalls below the charging band's low level, the application valve 234will be opened once again.

When the driver changes brake call, or the automatic blending programrequires it, the controller 68 may call for a change in retarder level.When this necessitates reducing the retarder pipe level, the retarderrelease valve 232 is opened by the controller 68 and retarder pipepressure is vented to atmosphere until the upper discharge dead bandlimit is reached, where discharge is terminated and both retarder pipecontrol valves 232 and 234 are lapped.

Although the present invention has been described and illustrated indetail, it is to be dearly understood that the same is by way ofillustration and example only, and is not to be taken by way oflimitation. The brakepipe control system, parking brake control systemand retard control systems have been described in combination to achievethe object of the invention. These systems may be used individually. Thespirit and scope of the present invention are to be limited only by theterms of the appended claims.

What is claimed:
 1. An electropneumatic brake control system for railvehicles interconnected by a brakepipe and a supply pipe and including aparking brake and a parking brake control system, said parking brakecontrol system comprising:a parking brake valve responsive to brakepipepressure for connecting said parking brake to either a supply port or anexhaust port of said parking brake valve for releasing said parkingbrake in response to an increase in said brakepipe pressure or applyingsaid parking brake in response to a decrease in said brakepipe pressure;and an electropneumatic valve for connecting said supply port of saidparking brake valve to a pressure from said supply pipe whende-energized and for connecting said supply port to atmosphere whenenergized.
 2. A system according to claim 1 including a controller forcontrolling said electropneumatic valve in response to operatorinitiated controls.
 3. A system according to claim 2 including atransducer for measuring the parking brake pressure and feeding it backto the controller.
 4. A system according to claim 1 wherein said parkingbrake is spring applied and pneumatically released and including aparking brake release pipe connecting said parking brake and saidparking brake valve.
 5. A system according to claim 4 including a valveconnecting the greater of the pressure of said parking brake releasepipe and said brake pipe to said parking brake for releasing saidparking brake.
 6. A system according to claim 1 including a check valvefor charging the supply pipe with the brake pipe.